First, I assume you're seeking help for the mental health issues? Because you will face stressful situations throughout your life - simply working less busy shifts or different jobs won't necessarily solve the problem.

If you're currently working through the underlying issues that cause the dissociation with a psychological professional, and you need a solution in the meantime, I would try talking to your boss about working different shifts. Maybe you'll still need to work the busy shifts from time to time, but if you can get a few shifts in the morning/afternoon (when fewer people are around), that might help. Additionally, you could try writing down the orders as soon as you hear them. That may slow you down with processing the orders, but at least it will give you something to look at. Also, one thing I recently learned about dissociating (due to trauma and other issues) is that it helps to have a "grounding kit." This kit should include five items, one thing to address each of your five senses. For example, you could carry an object or piece of fabric that "brings you back" to the present. A bracelet with an interesting texture can be rubbed and serve as a "grounding tool" when you begin to dissociate. If you haven't already learned about this concept in therapy, I suggest bringing it up and brainstorming!